Mass balance of the Greenland ice sheet (2003–2008) from ICESat data – the impact of interpolation, sampling and firn density

Abstract

ICESat has provided surface elevation measurements of the ice sheets since the launch in January 2003, resulting in a unique dataset for monitoring the changes of the cryosphere. Here, we present a novel method for determining the mass balance of the Greenland ice sheet, derived from ICESat altimetry data. <br><br> Three different methods for deriving elevation changes from the ICESat altimetry dataset are used. This multi-method approach provides a method to assess the complexity of deriving elevation changes from this dataset. <br><br> The altimetry alone can not provide an estimate of the mass balance of the Greenland ice sheet. Firn dynamics and surface densities are important factors that contribute to the mass change derived from remote-sensing altimetry. The volume change derived from ICESat data is corrected for changes in firn compaction over the observation period, vertical bedrock movement and an intercampaign elevation bias in the ICESat data. Subsequently, the corrected volume change is converted into mass change by the application of a simple surface density model, in which some of the ice dynamics are accounted for. The firn compaction and density models are driven by the HIRHAM5 regional climate model, forced by the ERA-Interim re-analysis product, at the lateral boundaries. <br><br> We find annual mass loss estimates of the Greenland ice sheet in the range of 191 ± 23 Gt yr<sup>−1</sup> to 240 ± 28 Gt yr<sup>−1</sup> for the period October 2003 to March 2008. These results are in good agreement with several other studies of the Greenland ice sheet mass balance, based on different remote-sensing techniques

Mass loss of Greenland's glaciers and ice caps 2003–2008 revealed from ICESat laser altimetry data

“…The mean surface elevation changes were estimated at 500 m along track resolution and associated with variance from the regression procedure (cf. [Sørensen et al, 2011]). In addition, we assume that the error within each 500 m segment remains constant and, hence, the variances should reflect both the error of the measurements and the accuracy of the fit.…”

“…We performed the following data culling and correction procedures to reduce systematic errors and outliers (cf. [Sørensen et al, 2011], method M3, for full details): (a) a saturation correction to reduce elevation estimation errors originating from the saturation of the waveform as to reduce systematic errors in the measurements, (b) identification of thresholds of the socalled IceSvar parameter-showing the difference between the return signal and a Gaussian functional fit-to reject data with a large misfit (cf. [Smith et al, 2009]), and (c) identification and elimination of data with multiple peaks.…”

“…[9] The derivation of the firn compaction follows Sørensen et al [2011], where the change in the air space of the top firn (top 15 annual layers) is estimated from a dynamic firn model based on the description of firn compaction by Herron and Langway [1980] and Arthern et al [2010]. The dynamical firn model is forced by interpolated output fields from the HIRHAM5 regional climate model at a resolution of 5 Â 5 km [Lucas-Picher et al, 2012].…”

“…Here we report the elevation changes over the October 2003 to March 2008 period for the GIC on Greenland based on processed ICESat data [cf. Sørensen et al, 2011] and the new GIC inventory [Rastner et al, 2012]. Our focus is on the regional variability, a differentiation between marine and land-terminating glaciers, and an adequate consideration of firn compaction and density differences.…”

“…[3] A large number of studies have estimated the overall mass budget for Greenland (ice sheet including GIC to a varying degree) based on Gravity Recovery and Climate Experiment (GRACE) data (e.g., [Velicogna, 2009;van den Broeke et al, 2009]), altimetry data (e.g., [Sørensen et al, 2011;Pritchard et al, 2009]), or mass balance modeling . However, the contribution of the GIC alone has not been assessed so far despite their potentially high contribution to SLR.…”